We love our scooters! DH rides his to work everyday (excluding rain or snow) and I ride mine all summer until school starts again. I strapped a basket to the back of mine (an old metal gym locker basket) so when I go to the store, I know if it fits in the grocery carry style basket, it will all fit between my basket and backpack.
DH has a Yamaha Zuma and loves it. It's a little bigger and heavier but he thinks that makes it a little more stable. Mine is a Tank (not sure who makes it). I like it but have had problems.
As has been suggested, find a good dealer and test drive a few to find the weight and size that is good for you. If you want some extra help, find out if anyone is offering a motorcycle class near you, they might let you come for their practice day (here they have a day set aside for cones and the like outside for people to practice turning, stopping and starting).
As far as the speed, scooters are not technically supposed to be on highways. If the speed limit is 55, it is off limits to scooters. At least that's the law here ... They can't get up to speed quickly enough and most are not even capable of reaching 55 due to a lower CC value (thus the reason for not needing a cycle or other special license). Because you might not be able to find a yellow one you like, you can also look at getting an orange reflective vest. They carry them at most running stores. Even though mine is a bright, neon green, I wear a bright orange sweatshirt because they see me before they see my scooter.